The invention relates to a method for correcting the pre-programmed initiation of an event in a spin-stabilized projectile, a device for executing the method, and a use of the device.
Methods and devices of this type are used in connection with the chronologically pre-programmed initiation of functions in a spin-stabilized ballistic projectile, wherein initiation of the function is intended to take place at a defined initiation place and therefore at a defined initiation distance from the launch location, or respectively at a defined initiation time, and therefore after a defined length of flight. The function which is to be initiated in this way can be any arbitrary function; with ballistic projectiles the time of disaggregation into partial projectiles, or respectively of fragmentation, is generally determined in this manner.
It has been long known in connection with projectiles of different types, i.e. not only ballistic projectiles, to utilize a time fuse with a fixed or adjustable initiation time for determining the initiation time, wherein projectiles with time fuses with adjustable timing are designated as so-called fuse-time-fixed projectiles.
In principle, two types of time-fixed fuses can be used in spin-stabilized projectiles, namely time fuses and rotary fuses. With time fuses, the disaggregation is initiated at the end of a defined, or respectively definable time interval which, for example, starts at launch; with rotary fuses, disaggregation is initiated after a defined, or respectively definable number of revolutions which the projectile has performed since the launch.
Several methods are known for setting the time fuse, or respectively for the so-called fuse-time-fixing of fuse-time-fixed projectiles. In this case a basic distinction needs to be made between projectiles, wherein fuse-time-fixing takes place in a defined manner prior to launch on the basis of theoretical calculations, and projectiles, wherein fuse-time-fixing takes place after the launch, wherein deviations from theoretically calculated values, for example for the disaggregation location, the disaggregation time, the muzzle velocity or, if required, the final angle of twist, can be taken into consideration. The variation range of one of these parameters, for example of the muzzle velocity or of the final angle of twist, normally lies in a range of less than 5%.
With projectiles which can be fuse-time-fixed during flight, it is possible to provide the fuse with the time of disaggregation by remote signaling, for example. However, such devices have various disadvantages; for one, they require an elaborate implementation of a receiver, and secondly, there is the danger of enemy interference with the remote signaling processes, which can result in incorrect fuse-time-fixation. These disadvantages are so serious that it is therefore often preferred to provide only a pre-programmed fuse-time-fixation, which is not affected anymore during flight, so that no remote signaling connection is required.
Pre-programmed rotary fuses are pre-programmed, preferably during loading, in such a way that ignition takes place after a defined, preset number of revolutions of the projectile. However, without corrective measures, such pre-programming has comparatively inaccurate results, since it cannot take the into consideration deviations, based on the actual flight characteristics of the projectile, from the theoretically determined flight characteristics.
It is known to everyone skilled in the art that the muzzle velocity is an essential value determining the flight characteristics of the projectile. Generally, the effective muzzle velocity deviates for various reasons from the theoretically calculated muzzle velocity, which has the result that the effective location/time of the disaggregation of the projectile differs from the desired location/time of the disaggregation which, for example, had been theoretically determined.
To prevent, or at least limit, such deviations, while still not providing an elaborate remote signaling device, various steps can be taken which are based on detecting the effective frequency of revolutions of the projectile and/or the effective muzzle velocity of the projectile, which is correlated with the effective frequency of revolutions, and including them internally in the projectile in determining the time-fixed fuse time.
Various methods are known for determining the effective muzzle velocity.
For example, the effective muzzle velocity can be detected on the outside of the gun barrel closely near its muzzle by means of a coil arrangement with two spaced-apart measuring coils. However, such measuring coils are comparatively delicate and constitute a particularly endangered component, at least with mobile guns.
The effective muzzle velocity can also be determined by extrapolation from a projectile velocity measured inside the gun barrel in the area of its muzzle cross section. Here, measurement is performed with the aid of two sensors, which are arranged at a defined mutual distance from each other. The disadvantage is that comparatively elaborate devices at the gun barrel are required for executing this method, and that the results are not very accurate as a result of the extrapolation.
In order to avoid the disadvantages of the above mentioned methods for determining the actual muzzle velocity, attempts are also made to determine the actual muzzle velocity of the projectiles after they have been fired, but without additional devices at the gun barrel.
Since there is a fixed connection between the projectile velocity and the frequency of projectile rotation in the flight phase immediately following firing, attempts are made to correlate the time of the disaggregation of the projectile, instead with the projectile velocity, with the corresponding number of revolutions made by the projectile in the course of its flight along its trajectory.
Counting of the rotations of the projectile is performed with the aid of the earth magnetic field in conventional methods of this type. The fuse has a counter, which continuously integrates the number of the projectile revolutions. By means of the spin of the projectile, for example its rotation essentially around the longitudinal axis of the projectile, a voltage is induced inside the fuse, for example in a coil arranged for this, by means of the earth magnetic field, which extends sine-like over time. The counter continuously, i.e. during the complete duration of the flight of the projectile, adds up the number of pulses between two crossovers of this voltage in the same direction. With a fuse which, as mentioned above is called a rotary fuse, ignition, or respectively the disaggregation of the projectile takes place as soon as the number of added-up pulse s has reached a pre-programmed value.
This method has several disadvantages. Counting of the revolutions of the projectile takes place either during its entire time in flight, or only directly following its firing, but with a check afterwards, for example after 80% of the approximate time in flight. Since the voltage induced by the earth magnetic field is only usable if it is amplified, and since energy is needed for this amplification, it is necessary to provide a considerable amount of energy for this amplification because of the comparatively long use of the earth magnetic field Furthermore, interferences with the voltage process induced by the earth magnetic field and of the values derived therefrom can be caused by interfering enemy transmission; the effects of these interferences are the more important, the longer the use of the earth magnetic field lasts.
For example, a multi-functional fuse for spin-stabilized projectiles has become known from EP 0 661 516 A1, wherein the actual muzzle velocity is calculated on the basis of the actual frequency of rotation of the projectile. The earth magnetic field is used for determining the frequency of rotation, wherein each rotation of the projectile provides a pulse. The number of rotations is counted during a defined period of time, which is determined by an oscillator inside the projectile in that the number of the rotations of the projectile are added up. The actual muzzle velocity is determined here in accordance with the following equation (1):
V0s=(N1s*xcfx80* Ds)/(Ts*tg(xcfx86es))xe2x80x83xe2x80x83(1)
The indices xe2x80x9ctxe2x80x9d were inserted into this equation in order to make it clear that the terms used therein are those which were obtained from the prior art as described by the mentioned EP 0 661 516 A1, and in order to prevent mixups with the designation of further equations relating to the invention The meanings in equation (1) are
VOs the muzzle velocity calculated on the basis of the measurement
Ts the measuring time
N1s the measured number of rotations of the projectile
xcfx86es the final angle of twist
Ds the caliber
Tg the tangential function
Inter alia, it is proposed in EP 0 661 516 A1 to perform the continuous determination of the length of flight, or respectively of the trajectory, during a first flight phase of approximately 1000 meters by means of the rotation of the projectile; at the beginning of a second flight phase, starting approximately after 1000 meters, a change should then be made from counting the rotation to counting the time, since it is said to have been shown that, although the accuracy of rotary fuses is quite good over flight distances up to 1000 meters, at greater flight distances it was inferior to the accuracy of time fuses.
Thus, the earth magnetic field is used for the continuous counting of the projectile revolutions during the comparatively long first flight phase of 1000 meters, or respectively during the amount of time required for flying over this distance. Interferences with the earth magnetic field therefore can affect the counting over a very long time and greatly compromise the function of the fuse.
Thus, the object of the invention is seen in
proposing an improvement of the method of the type mentioned at the outset, by means of which the disadvantages of the prior art are prevented,
producing a device for executing this method, and
proposing a use for this device.
It is pointed out here that the novel method in accordance with the following description is based on effects resulting in projectiles because of the actions of a magnetic field, wherein the earth magnetic field is always mentioned as example, however, corresponding effects can also be caused by other, i.e. artificially created, magnetic fields.
It is moreover pointed out that in what follows reference will be made to the initiation of the disaggregation of a projectile, however, the disaggregation is only an example of the pre-programmed events in projectiles which can be corrected in accordance with the method of the invention.
In accordance with the invention, the measurement for determining the frequency of rotation of the projectile only takes place during a comparatively brief period of time immediately following the firing of the projectile, which is called the calibration phase. The novel method provides comparatively good results, because during the calibration phase the projectile velocity differs only to a very small degree from the muzzle velocity determined on the basis of the frequency of rotation of the projectile. It is furthermore advantageous that the effects of interferences of the earth magnetic field remain small, since it only takes effect during the relatively short calibration phase. A further advantage of the chronological limitation of the use of the earth magnetic field by the invention lies in that the energy needed for signal amplification in the fuse is low.
Following the calibration phase, everything else inevitably occurs in the projectile, or respectively without the possibility of exerting any influence from the outside. Although the novel method is therefore not an iterative method, since no attempts to affect the events in the fuse after the calibration phase, for example in order to take into consideration newly occurring meteorological effects or changes in the flight path of the targets, it is still comparatively accurate, since the ballistic behavior of the projectiles and of the targets in flight within the comparatively short time periods of the length of flight is sufficiently known or then becomes unimportant.
It is easy to understand that the details of the calculations required for executing the method in accordance with the invention can be performed in different ways, or respectively with the aid of different devices.
By means of the method in accordance with the invention the calibration phase is preferably calculated, namely in such a way that the overall error from the relevant unavoidable errors becomes as small as possible. The performance of such a calculation will be described in what follows. The prerequisites and simplifications performed in the course of such a calculation do of course affect its accuracy. As usual, greater accuracy must be paid for with a larger outlay.
The accuracy of the determination of the muzzle velocity essentially is a function of the number of rotations of the projectile during which the measurement, or respectively counting of the pulses of the oscillator, or respectively frequency generator, inside the projectile takes place. If measuring is performed during a large number of rotations of the projectile, the measuring method per se is more accurate, since the influence of uncounted pulses, in particular at the start and the end of the measurement, is relatively reduced. Thus, in order to keep the errors of the measurement method small, measurement during a large number of rotations of the projectile is advantageous. However, along with the number of the rotations of the projectile the length of time during which the projectile moves forward is also increased, wherein it loses velocity and frequency of rotation, which also results in an error which could only be corrected by means of a considerable computing outlay. In order to keep the error connected with the reduction in velocity small, the measurement of the least possible number of rotations of the projectile is therefore advantageous. Since the first-mentioned error is reduced with an increasing number of rotations of the projectile, but the second error mentioned increases with an increasing number of rotations, there is an optimal number of rotations of the projectile at which the sum of the mentioned errors, or respectively the overall error, is minimal. This optimal number of rotations of the projectile is determined by means of the following calculation.
In this case it is assumed that the use of the earth magnetic field takes place in the sense that the number of pulses from a pulse generator, or respectively oscillator, inside the projectile is measured, or respectively added up, in the course of a defined number of rotations of the projectile. However, it is pointed out that other methods are also possible for determining the effective frequency of rotation or the effective muzzle velocity of the projectile, while making use of the earth magnetic field, and that the progress achieved by means of the invention is not intended to be limited to this measuring, or respectively calculation method, but is to be seen as the large reduction of the period of time during which the earth magnetic field is used.
The first relative error is determined as follows: an oscillator with a fixed oscillator frequency inside the projectile provides M pulses while the projectile performs a defined number of rotations, wherein M is calculated in accordance with the following equation (2):
M=(fz*xcfx80*D*R)/(V0*tg(xcfx86e))xe2x80x83xe2x80x83(2)
The following meanings apply in respect to equation (2) and further equations:
M the number of counted pulses of the oscillator inside the projectile
R the number of rotations of the projectile during which the pulses of the oscillator are counted
VO the actual muzzle velocity
e the final angle of twist
D the caliber
fz the constant frequency of the frequency generator, or respectively oscillator, inside the projectile
tg the tangent function.
If xcex94M pulses are not counted during the count, the relative first error is
xcex94M/M=((xcex94M*V0*tg(xcfx86e))/(fz*xcfx80*D))*1/Rxe2x80x83xe2x80x83(3)
Thus, as ascertained above, the first relative error decreases with increasing R.
The second relative error relates to the deviation of the trajectory, or respectively the time in flight, from the theoretical value, and is calculated in accordance with the following equation (4):
xcex94s/s=((xcfx80*D*(axe2x88x92k))/(2*tg(xcfx86e)))*Rxe2x80x83xe2x80x83(4)
The following meanings apply:
s the distance theoretically traveled by the projectile
xcex94s the difference between the distance theoretically traveled by the projectile and the actually traveled distance
(2axe2x88x92k) a correction term, wherein a is the Antonio factor.
Thus, as ascertained above, the second relative error increases with increasing R.
The relative overall error, which is identified by therefore is in accordance with equation (5):
xcex5=xcex94M/M+xcex94s/s=((xcex94M*V0*tg(xcfx86e))/(fz*xcfx80*D))*1/R+((xcfx80*D*(2axe2x88x92k))/(2*tg((xcfx86e)))*Rxe2x80x83xe2x80x83(5)
In order to find that optimal value of the projectile revolutions Ropt, at which is minimal, xcex5 is differentiated toward R, and the result of this differentiation, i.e. dxcex5/dR, is set to zero. The R which can be calculated from this corresponds to the sought after Ropt.
dxcex5/dR=xe2x88x921/R2*((xcex94M*V0*tg((xcfx86e))/(fz*xcfx80*D))+((xcfx80*D*(2axe2x88x92k))/(2tg((xcfx86e)))=0xe2x80x83xe2x80x83(6)
Ropt2=(tg(xcfx86e))/(xcfx80*D))2*(2*V0*xcex94M)/(fz*(2axe2x88x92k))xe2x80x83xe2x80x83(7)
Ropt is finally found by finding the root from Ropt2. It is not possible to define an Ropt of the type of an invariable characteristic number. Even by means of the simplifications made on the basis of this, Ropt can only be calculated while taking the respective geometric conditions, such as the caliber D and the final angle of twist e, as well as the respective muzzle velocity VO, into consideration.
The above calculation of Ropt took place by means of several simplifications. In particular, in the equation for the factors by which 1/R, or respectively R, are multiplied, are considered to be constant, which in actuality only applies directly following firing. The following exemplary calculation of Ropt for a usual case will show, however, that Ropt is so small, that the mentioned simplifications are tolerable within the scope of the accuracy of the entire method. By means of
M=2 pulses
fz=1 MHz
VO=1050 m/sec
(2axe2x88x92k)=71.2*1/1 000 000
D=35 mm
xcfx86e=6.5
the value
Ropt=8 rotations of the projectile
is obtained for the optimal number of rotations of the projectile, during which the pulses of the oscillator should be counted.
Here, eight rotations of the projectile correspond to a distance of approximately 10 meters, which the projectile travels on its trajectory. In this exemplary case the earth magnetic field is therefore used in accordance with the above calculation over a trajectory of approximately 10 meters. But with the known method, the earth magnetic field is used over a trajectory of 1000 meters, i..e a distance 100 times longer, and therefore over a period of time which is more than 100 times longer. It is obvious that the method of the invention is much more accurate than the known method, because the drop in velocity is unimportant during the limited number of rotations of the projectile, and since an interference with the earth magnetic field has an effect only during a very limited calibration phase and therefore results in considerably smaller errors than with the known method. This even applies when it is considered that the above calculation contains numerous simplifications and inexactnesses.
As already mentioned several times, the earth magnetic field is used in connection with the novel method, the same as with conventional methods, for determining by way of the effective rotation frequency of the projectile the effective muzzle velocity of the projectile. The conventional method operates in such a way that each rotation of the projectile provides a pulse, and that the rotations of the projectile are counted during a defined time interval, which is determined by an oscillator inside the projectile, by adding up the pulses caused by the rotation of the projectile. The actual muzzle velocity is here determined in accordance with equation (1). The muzzle velocity VOs calculated in this way is directly proportional to the measured value, i.e. to the measured value of the number of rotations of the projectile. In spite of this, this measuring method is not very accurate because of the low resolution. In contrast thereto, in accordance with the invention the following procedure is preferably followed, wherein the pulses of a frequency generator, or respectively oscillator, inside the projectile are measured, or respectively counted, over a defined number of rotations of the projectile, and the calculation of the actual muzzle velocity is then performed in accordance with the following equation (8):
V0=(fz*xcfx80*D)/(tg(xcfx86e)*R)xe2x80x83xe2x80x83(8)
Because of the better resolution, more accurate results are obtained by means of this preferred variation of the novel method than with the known method, although the muzzle velocity to be calculated is only indirectly proportional to the measured value, i.e. the measured, or respectively added up, number of pulses of the oscillator inside the projectile.
The number of pulses of the frequency generator per rotation of the projectile are measured, or respectively added up, in that the change of the position of the projectile, i.e. the rotation of the projectile, is determined in the course of its rotation by means of the change in a voltage in a suitably placed coil arrangement in the projectile, which voltage is induced by the earth magnetic field. It should again be mentioned here that in place of the physical properties of the earth magnetic field, it is also possible to use the physical properties of another magnetic field for determining the rotation of the projectile.
As already mentioned, the approximate relationship VO/VO less than 5% applies for the deviation of the actual muzzle velocity from the theoretical muzzle velocity. In a simplifying way it is assumed for the further calculations that the resistance value for the projectile, which per se is a function of the velocity, is constant, which is permissible because of the mentioned relationship.